1. Field of the Invention
The field of the present invention is cosmetic product dispensers, particularly tube-style dispensers used for dispensing viscous or semi-viscous cosmetics.
2. Background
Dispensers for viscous or semi-viscous cosmetics, such as lip gloss, come in many forms, from the basic squeeze tube to mechanisms that rely on a piston and vial combination. In the latter type of dispensers, a lead screw drives and causes the piston to translate within the vial, thereby applying pressure to the bulk product within the vial and forcing the product out of the applicator head. The key to operation in these types of dispensers is to keep the piston from rotating, so that when the lead screw rotates, the piston does not rotate, but instead translates within the vial.
Various techniques have been applied to eliminate rotation of the piston as the lead screw rotates. One technique is to use an oval piston with the inside of the vial also being oval shaped. While this works, it can change the aesthetics of the package and introduce complexities in the assembly process because an oval piston must be properly oriented before it can be inserted into the oval interior of the vial. Obtaining a good seal between the oval piston and the vial can also be problematic as dimensions are harder to control on oval plastic parts due to material shrinkage.
A second technique is to increase interference between the piston seal and the inner wall of the vial. This technique can have two negative results. The first is that it increases the force needed to translate the piston via the lead screw. This leads to the necessity of applying a greater torque to the lead screw in order to dispense the product, and such a requirement may lead directly to increased consumer dissatisfaction with the dispenser and the product. The second negative impact is that the increased interference relaxes with heat and time, and sometimes to a point in which insufficient interference remains to prevent the piston from rotating.
A third technique that has been used is the addition of vertical flats or ribs running the length of the inside of the vial. Such features, however, interrupt the smoothness of the inner wall, and a smooth inner wall is preferred for creating an effective seal with the piston. Without a smooth inner wall, undesirable leakage of the product may occur within the vial. In addition the piston seals may relax against these features over time or when exposed to elevated temperatures, thereby reducing the amount of interference between the piston and the inner wall and allowing the piston to spin.
In view of the shortcomings of these known techniques, a new design for this type of dispenser is desirable, one which eliminates rotation of the piston as the lead screw rotates and overcomes one or more of these shortcomings.